1. Field of the Invention
The present invention relates generally to an apparatus for controlling unwanted sedimentation within estuarine harbors. More particularly the invention concerns a novel apparatus comprising a segmented, pneumatic spar curtain which extends across the mouth of a quiet water berthing area and prevents the intrusion of flocculated clay sediments and the like into the area.
2. Discussion of the Prior Art
Effective control of sediments within quiet water marine facilities has presented substantial difficulties. For the most part these unwanted sediments are transported by rivers in a largely dispersed state, but upon reaching the more saline estuarine waters, they flocculate and become concentrated in the lower region of the water column. The sediment is then moved about by tidal and other currents until reaching quiet water areas, where it settles out and is deposited on the bottom.
Present methods of controlling unwanted sedimentation within estuarine harbors generally consists of periodically removing the accumulated sediment using conventional hydraulic or mechanical dredges. Several prior art inventions are directed toward methods and apparatus for such purposes. For example, U.S. Pat. No. 3,486,253 discloses a floating earthmoving device and U.S. Pat. No. 3,629,963 discloses an apparatus for leveling the floor of harbor areas. However, these types of methods are rapidly becoming uneconomical because of rising energy costs and because of the decreasing availability of nearby disposal sites.
Recently, the development of alternatives to dredging methods has begun. One method which has shown considerable promise has been the passive curtain barrier concept. The curtain acts to exclude the sediment-ladened bottom water from the protected area by forming a tight seal along its bottom and sides. The vertical stratification of the waters prevents the bottom water from over-topping the curtain barrier. The surface waters, however, are free to move in and out of the berthing area with the tide. One problem which has hindered full utilization of this concept has been the lack of an efficient method of opening and closing the curtain to accomodate transiting vessels. Various suggestions have been made for opening and closing the curtain barrier, including apparatus which rely on a tidal coordinated lifting procedure. Such approaches typically use equipment which embodies large surface floats and adjustable lengths of lifting chains. However, these approaches for opening and closing the curtain have proven generally unsatisfactory being both time consuming and labor intensive. The curtain has to be opened and closed at high tide and a full cycling of the curtain requires three separate visits by harbor personnel, namely a visit at low tide to shorten the chains; a visit at high tide to open the curtain; and, after moving the vessel into the berth and closing the curtain, a visit at low tide to once again lengthen the chains. Another difficulty with this method is that the actual opening and closing of the curtain must be accomplished using a small vessel.
Various other approaches for controlling unwanted sedimentation, including flotation barrier concepts, have been suggested. For example U.S. Pat. No. 3,984,987 discloses a floating barrier apparatus for accomplishing silt and pollution control. U.S. Pat. No. 3,708,983 discloses a series of air-retaining structural units connected together in a complete loop and U.S. Pat. No. 3,691,773 discloses a water barrier flotation curtain comprising a barrier having a sandwich-like construction. However, each of these prior art approaches has proven unsatisfactory for practical, cost effective control of sedimentation in quiet water berthing areas.
Applicant is also familiar with the following prior art patents which represent the closest art known to applicant and which serve to vividly demonstrate the uniqueness of the invention described and claimed hereinafter:
U.S. Pat. No. 3,640,073 -- Frank J. Samsel PA1 U.S. Pat. No. 3,974,655 -- Halpern et al PA1 U.S. Pat. No. 4,248,547 -- Norman D. Brown